In the related art, LP-CVD (Low Pressure Chemical Vapor Deposition) is used in forming a film such as a silicon oxide film or the like. In the film formation using the LP-CVD, a film having a desired thickness is formed by supplying a gas, the flow rate of which is adjusted to a constant value, into a pressure-controlled reaction chamber for a predetermined time.
In recent years, the structural change or miniaturization of a semiconductor device poses a problem in that the conventional process cannot be directly applied because the coverage performance is low under the conventional LP-CVD film forming conditions. This problem is particularly true when film formation is performed with respect to a pattern of a STI (Shallow Trench Isolation) shape or a hole shape which has a high aspect ratio. In the LP-CVD film formation, there is a demand for the reduction of an impurity concentration in a film. Thus, a demand has existed for a method of forming a thin film having good properties.